There have been manufactured a large number of liquid crystal display elements utilizing optical (refractive index) anisotropy (Δn) and dielectric anisotropy (Δ∈) characteristic of liquid crystal compounds. The liquid crystal display elements have been widely applied to clocks, calculators, various measuring instruments, automotive panels, word processors, electronic notebooks, portable phones, printers, computers, TV sets, and the like, with demand increasing year by year. A liquid crystal compound exhibits a characteristic liquid crystal phase between a solid phase and a liquid phase. The liquid crystal phase is roughly classified into nematic phase, smectic phase, and cholesteric phase, of which nematic phase is currently most widely used for display elements. Regarding to techniques applied to liquid crystal displays, as a display mode, there have been a large number of proposals, and currently known modes include, for example, dynamic scattering (DS), guest-host (GH), twist nematic (TN), super twist nematic (STN), thin film transistor (TFT), ferroelectric liquid crystal (FLC), and the like, while as a driving system, there are known static driving, time-division driving, active matrix driving, dual-frequency driving, and the like.
In common liquid crystal displays such as TN and STN, which have been conventionally widely used, the electric field generated for reorientation is substantially perpendicular to the liquid crystal layer. In contrast, in in-plane switching (IPS) mode, the electric field has a significant component parallel to the liquid crystal layer.
In IPS liquid crystal displays, by applying the electric field generated using comb electrodes on one substrate, liquid crystal molecules constituting a liquid crystal layer oriented almost parallel to the substrate surface are rotated within a plane almost parallel to the substrate, and the display function is based on the birefringence of the liquid crystal layer. Such displays are proposed, for example, in Patent Documents 1 to 5 and others.
IPS displays have advantages such as a wider viewing angle and a lower load capacity as compared with conventional TN displays resulting from the in-plane switching of liquid crystal molecules, thereby extending the application to monitor, television sets, and the like having larger display area.
A liquid crystal composition used for IPS liquid crystal displays is required to have a low rotational viscosity (γ1) enabling fast response. Moreover, it is effective to increase the electrode spacing in order to increase the numerical aperture for improving the brightness of displays, but in such case the threshold voltage due to the structure of IPS cells increases. To suppress this drawback, liquid crystal compositions having a high dielectric anisotropy (Δ∈) are needed.
However, with conventionally known liquid crystal media, no liquid crystal composition with satisfactory performances has been yet attained.
For example, Patent Documents 6 and 7 and others propose a liquid crystal composition comprising a trifluorobenzene derivative for IPS liquid crystal devices; however, this liquid crystal composition is still unsatisfactory.
Patent Document 8 proposes an active matrix liquid crystal display using a liquid crystal whose specific resistance is not more than 1×1014 O·cm and not less than 1×109 O·cm; however, the liquid crystal display is still unsatisfactory.
Further, it is expected that the market of liquid crystal display elements will develop in the field of portable information terminals such as portable phones, in which performances such as low power consumption are demanded. In this field, low voltage-driven TN liquid crystal displays are applied, and a liquid crystal composition used here is required to have a high dielectric anisotropy (Δ∈) for decreasing the threshold voltage and a low rotational viscosity (γ1) for increasing the response speed. Various liquid crystal compositions have been studied to meet such demands. No satisfactory composition, however, has been realized yet.    Patent Document 1: Japanese Patent Laid-Open Publication No. S56-91277    Patent Document 2: Japanese Patent Application Laid-Open No. H5-505247    Patent Document 3: Japanese Patent Laid-Open Publication No. H6-160878    Patent Document 4: Japanese Patent Laid-Open Publication No. H7-225388    Patent Document 5: Pamphlet of International Publication No. 2004/053582    Patent Document 6: Japanese Patent Laid-Open Publication No. H10-245559    Patent Document 7: Japanese Patent Laid-Open Publication No. H11-29771    Patent Document 8: Japanese Patent Laid-Open Publication No. H7-306417